Substrates for use in the field of flat panel displays (hereinafter generally referred to as “FPDs”) or the like are often made of glass. Electronic devices having the FPD mounted thereon, such as cellular phones and notebook PCs, constantly need to be lighter, thinner, and durable. Depending on the purpose of use, flexibility is further needed. It is difficult for a glass substrate to meet these needs. Therefore, a consideration has been made to change the glass substrate to a plastic substrate.
However, when changed to the plastic substrate, handling thereof becomes difficult due to flexibility thereof, thus causing the problem that it is difficult to use an existing production facility.
Patent Document 1 describes a structure that makes it possible to handle the plastic substrate in the existing production facility by using a thermosensitive adhesive. That is, according to Patent Document 1, the plastic substrate is temporarily secured to a glass base by interposing therebetween the thermosensitive adhesive whose adhesive strength is reversibly controllable by heat. Then, after a functional film is deposited on a surface of the plastic substrate, temperature is lowered to reduce the adhesive strength of the thermosensitive adhesive, and the plastic substrate with the functional film is then peeled off from the glass base to obtain an object.
However, the handling performance during a process is not taken into consideration in the conventional thermosensitive adhesive as described in Patent Document 1. Therefore, handling defectiveness may occur during the process.
In addition to the handling performance, the following is needed for the thermosensitive adhesive used for temporarily securing the plastic substrate. That is, chemical resistance in photolithography, washing process, or the like is needed. Depending on the process, the thermosensitive adhesive may be exposed to a high-temperature atmosphere exceeding 100° C., and hence heat resistance is also needed. Specifically, it is necessary to suppress floating of the substrate in the high-temperature atmosphere, and it is also needed to suppress a dimensional change of the substrate due to a temperature change from room temperature to high temperatures. Furthermore, easy peeling property needs to cope with an occasion that a peeling stress increases with increasing substrate size. The conventional thermosensitive adhesive failed to sufficiently cope with these needs.